BOSTON — The Penguins are improving at putting more shots on net. They just need to put more into the net.

And they’re running out of time.

Pittsburgh forced Boston goalie Tuukka Rask to make 53 saves, but the Bruins won 2-1 in double overtime on Wednesday night to take a 3-0 lead in the Eastern Conference finals.

The Penguins, who averaged 4.27 goals per game through the first two playoff rounds, have totaled two scores through the first three games against the Bruins.

The Penguins must keep firing pucks at Rask, forward Pascal Dupuis said Thursday, and “with the firepower that we have on our team, eventually they will go in.”

If “eventually” doesn’t come tonight, their season will be over in stunning fashion. The team of Sidney Crosby, Evgeni Malkin and other top offensive threats will have been swept in the best-of-seven series.

It would be a shocking end to a season in which the Penguins led the NHL in scoring, but have been outscored 11-2 in the three losses to the Bruins.

Only three teams have overcome 3-0 playoff deficits. The Penguins know the odds are stacked heavily against them but are trying to ignore that.

“I think if you’re betting right now, you’re not betting on the Penguins down 3-0,” said forward Brandon Sutter, who has one of their two goals. “But we’re not going to quit. The percentages are, obviously, against us, but we’ve got a good team.”

The top-seeded Penguins were dominated by the fourth-seeded Bruins in the first two games, losing 3-0 and 6-1. But in Game 3, they outplayed Boston for much of regulation.

“We need to be the team who we believe we are and go back to what’s made us successful,” forward Matt Cooke said. “Obviously, the result wasn’t there, but the effort and determination and style of play was more like who we are.”

The Bruins won when Patrice Bergeron, covered closely by defenseman Brooks Orpik, redirected Brad Marchand’s pass behind goalie Tomas Vokoun at 15:19 of the second overtime.

An inch or two either way, and the pass might have missed Bergeron’s stick or his shot could have gone wide of the net.

“He drove the net. He outbattled the guy,” said Bruins center David Krejci, the leading scorer in the playoffs. “It looked pretty simple, but it’s tough when you go to the net to keep your stick on the ice and he managed to do that and got a big goal.”

But the Bruins had their worst game of the series. They allowed too many shots, gave the puck away too often and didn’t score in regulation after Krejci connected just 1:42 into the first period.

“We’ve got to play a better game,” Boston coach Claude Julien said. “We might have won the game, but we’re certainly not pleased with the way we played. We know they played better, but I don’t think we did, and we’ve got to make sure we’re at the top of our game (today).”

The last team to lose a series after going up 3-0 was the Bruins in the Eastern Conference semifinals against the Philadelphia Flyers in 2010.

This year, Boston led Toronto 3-1 in the first round then lost the next two games and trailed 4-1 with 11 minutes left in the third period of Game 7 before winning 5-4 in overtime. In the next round, the Bruins led the New York Rangers 3-0, lost Game 4, then won Game 5.

“It’s not over until you close that fourth (win) out,” Boston’s Johnny Boychuk said. “At any point, the series can switch.”

And the Bruins don’t want to go back to Pittsburgh for Game 5 on Sunday night.

“You just have to have that killer instinct and just forget what happened in the past three games and just focus on that one game,” defenseman Dennis Seidenberg said. “Whenever we play in the moment we play our best hockey.”

Sidney Crosby’s hockey has been far from his best.

The NHL scoring leader has no goals and no assists in the series. His turnover led to Marchand’s goal just 28 seconds into Game 2.

“You just have to trust your game and know that when you absolutely need it the most, everyone is going to show up and bring it and kind of let everything happen,” said Crosby, Pittsburgh’s captain. “I thought again (Wednesday) we did a lot of good things and probably deserved better.”

The Penguins have been scoreless on the power play in the series. But one of the Bruins’ top penalty killers, center Gregory Campbell, is sidelined for the playoffs after breaking his right leg when he dove and blocked a shot by Malkin in the second period on Wednesday.

Without him, the Bruins must “focus in a little bit more and make sure we’re taking care of the pucks,” defenseman Torey Krug said.

But the Penguins need to score more whether they’re on the power play or at even strength. And Wednesday’s game showed that they’re getting closer to doing that.

“On any given night, some of the chances we had go in and it could be five or six goals,” Sutter said. “By no means are we going to panic about scoring goals.”